The invention generally relates to a method and apparatus for removing solids from aqueous wash solutions, and more particularly to a method and apparatus for removing solids from wash solutions used in hot jet-spray parts washers and the like.
Wash solutions are used in recirculating washer devices constructed for cleaning industrial parts. In these devices, the wash solution is usually sprayed across the device being cleaned at high pressure to help dislodge solids and residue from the components being cleaned. The wash solution is then discharged from the washer tank through a filter before returning to recycle through the washer.
The particular pump used in typical washer systems must be strong enough to move the solution through the filter while maintaining the necessary flow pressure for efficient washing. This is problematic because the degree of filtration provided by a device is usually proportional to the pressure drop across the device. Thus, in some circumstances, multiple pumps are used to separately pump wash solution trough filtering devices and to provide the necessary jet spray pressure. Multiple pumps substantially increase procurement and operational cost of the washer system.
Depending upon the particular application suitable filters are required in recirculating washer systems to provide the necessary filtering of the wash solution as desired. For processing wash solutions where significant quantities of oil are present, removal of the oil is a prerequisite for filtration for removal of solids. In parts washers, this can be accomplished by use of a suitable oil skimmer such as that taught in U.S. Pat. No. 5,053,145 dated Oct. 1, 1991. Using this type of filtration alone for the removing of solids from aqueous solutions has not proved satisfactory due to the high filter maintenance required for removal of the entire solids load.
During the wash operation, various particulate matter in addition to oils, including sand, dust, wear metals, carbon and other contaminants dislodge from the components being washed. These materials vary in size and density, depending upon the particular application, and accumulate in the washer system during wash cycles. Heavier materials may settle out of the wash solution and collect on the bottom surface of the washer. Of course, these materials eventually must be removed. Typically, up to 90% of the particulate matter dislodged from the component being washed during the washing process are coarse enough (larger than about 100 microns) to settle out of suspension in the washer storage tank used in the system. In addition, when a washer system is turned off overnight or between shifts, particulate matter may settle to the bottom of the washer storage container and accumulate to a sludge. High pump capacity, or additional pumps, may be required to dislodge the sludge. The cost of procuring, maintaining and operating these high power pumps can be very high.
To avoid operating problems such as increased pump wear and reduced quality of cleaning that result from buildup of dislodged particulate matter, it has conventionally been the practice to dispose of wash solutions at intervals as short as two weeks. At one time, it was common practice to discharge dirty solutions to the sewer system, clean the washer storage of accumulated solids and recharge the system with clean solution.
The enactment of environmental legislation, such as the Resource Conservation and Recovery Act (RCRA), has resulted in regulations which prohibit disposal of aqueous cleaners in sewers and the like and specifically require special handling of contaminated industrial wash solutions. Most common wash solutions must now be treated as hazardous waste and disposed of in suitable fashion.
The increasing costs of hazardous waste disposal and the limited space for hazardous waste storage have created a need to increase the service life of wash solutions and reduce the volume of contaminated wash solutions requiring disposal. One solution is to provide systems having increased filtering capabilities to allow aqueous wash solutions to be used for longer periods of operational life.
Whenever filtering is increased, however, the effective flow of the wash solution is attenuated as previously described. Thus, when filtering is increased it is often necessary to also increase pump power. In conventional washer systems having only one pump for each washer cabinet, this would require procurement of a larger pump or addition of additional pumps for each washer system. The cost associated with such a modification is often cost prohibitive for smaller businesses.
For these and other reasons, there is a need for a system and method of removing particulate matter from aqueous wash solution in existing washer systems that can extend wash solution operational life without compromising the efficiency of the wash cycle and without requiring expensive additional pumps. Water filtration is very old.